Field of the Invention
The present invention relates to an electrode material, an electrode, and a lithium ion battery.
Description of Related Art
In recent years, as a battery anticipated to have small size, light weight, and high capacity, a non-aqueous electrolytic solution-based secondary battery such as a lithium ion battery has been proposed and put into practical use. The lithium ion battery is constituted of a cathode and a negative electrode which allow the reversible insertion and removal of lithium ions, and a non-aqueous electrolyte.
Regarding a negative electrode material for lithium ion batteries, as a negative electrode active material, generally, a lithium-containing metal oxide allowing the reversible insertion and removal of lithium ions such as a carbon-based material or lithium titanate (Li4Ti5O12) is used.
On the other hand, regarding a cathode material for lithium ion batteries, as a cathode active material, generally, a lithium-containing metal oxide allowing the reversible insertion and removal of lithium ions such as lithium iron phosphate (LiFePO4) or an electrode material mixture including a binder or the like is used. In addition, the cathode in the lithium ion battery is formed by applying the electrode material mixture to the surface of a metal foil called a current collector.
Compared with secondary batteries of the related art such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries, lithium ion batteries have a lighter weight, a smaller size, and higher energy, and thus are used not only as small-size power supplies but also as large-size stationary emergency power supplies in portable electronic devices such as mobile phones and notebook personal computers.
In addition, recently, studies have been underway regarding the use of lithium ion batteries as high-output power supplies for plug-in hybrid vehicles, hybrid vehicles, and electric power tools, and batteries used as the high-output power supplies are required to have high-speed charge and discharge characteristics.
However, in these lithium ion batteries, there is a problem in that, for example, the electron conductivity of electrode materials including an electrode active material such as a Li-containing metal oxide allowing the reversible insertion and removal of lithium ions is low. Therefore, in order to increase the electron conductivity of the electrode materials, there has been proposed an electrode material for which the surfaces of electrode active material particles are covered with an organic compound that is a carbon source, and then are fired, whereby a carbonaceous film is formed on the surfaces of the electrode active material particles through the carbonization of the organic compound, and carbon in the carbonaceous film is interposed as an electron conductive substance (Patent Document 1). In addition, the technique of cathode active material miniaturization has been proposed to improve the insertion and removal reaction of lithium ions to enable the lithium ion batteries to be applied for the applications requiring high power (Patent Document 2).